java.lang.Object
- io.netty.channel.ChannelHandlerAdapter
- - io.netty.channel.ChannelInboundHandlerAdapter
  - - io.netty.channel.ChannelDuplexHandler
    - - io.netty.handler.flow.FlowControlHandler

All Implemented Interfaces:

ChannelHandler, ChannelInboundHandler, ChannelOutboundHandler
```
public class FlowControlHandler
extends ChannelDuplexHandler
```
The FlowControlHandler ensures that only one message per read() is sent downstream.
Classes such as ByteToMessageDecoder or MessageToByteEncoder are free to emit as many events as they like for any given input. A channel's auto reading configuration doesn't usually apply in these scenarios. This is causing problems in downstream ChannelHandlers that would like to hold subsequent events while they're processing one event. It's a common problem with the HttpObjectDecoder that will very often fire an HttpRequest that is immediately followed by a LastHttpContent event.
```
{@code
 ChannelPipeline pipeline = ...;

 pipeline.addLast(new HttpServerCodec());
 pipeline.addLast(new FlowControlHandler());

 pipeline.addLast(new MyExampleHandler());

 class MyExampleHandler extends ChannelInboundHandlerAdapter {
```
See Also:

ChannelConfig.setAutoRead(boolean)

Nested Class Summary

Nested Classes
Modifier and Type Class Description

private static class FlowControlHandler.RecyclableArrayDeque
A recyclable ArrayDeque.
- Nested classes/interfaces inherited from interface io.netty.channel.ChannelHandler
  ChannelHandler.Sharable

Field Summary

Fields
Modifier and Type	Field	Description
`private ChannelConfig`	`config`
`private boolean`	`dequeuing`	`true` while a `dequeue(ChannelHandlerContext)` loop is on the stack.
`private static InternalLogger`	`logger`
`private FlowControlHandler.RecyclableArrayDeque`	`queue`
`private boolean`	`releaseMessages`
`private int`	`unsatisfiedReads`	Number of unsatisfied downstream `read()` calls.

Constructor Summary

Constructors
Constructor Description

FlowControlHandler()

FlowControlHandler(boolean releaseMessages)

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`channelInactive(ChannelHandlerContext ctx)`	Calls `ChannelHandlerContext.fireChannelInactive()` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`.
`void`	`channelRead(ChannelHandlerContext ctx, java.lang.Object msg)`	Calls `ChannelHandlerContext.fireChannelRead(Object)` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`.
`void`	`channelReadComplete(ChannelHandlerContext ctx)`	Calls `ChannelHandlerContext.fireChannelReadComplete()` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`.
`private boolean`	`dequeue(ChannelHandlerContext ctx)`	Dequeues messages while auto-read is enabled or downstream reads are unsatisfied, and updates `unsatisfiedReads` accordingly.
`private void`	`destroy()`	Releases all messages and destroys the `Queue`.
`void`	`handlerAdded(ChannelHandlerContext ctx)`	Do nothing by default, sub-classes may override this method.
`void`	`handlerRemoved(ChannelHandlerContext ctx)`	Do nothing by default, sub-classes may override this method.
`(package private) boolean`	`isQueueEmpty()`	Determine if the underlying `Queue` is empty.
`void`	`read(ChannelHandlerContext ctx)`	Calls `ChannelHandlerContext.read()` to forward to the next `ChannelOutboundHandler` in the `ChannelPipeline`.

Methods inherited from class io.netty.channel.ChannelDuplexHandler
bind, close, connect, deregister, disconnect, flush, write

Methods inherited from class io.netty.channel.ChannelInboundHandlerAdapter
channelActive, channelRegistered, channelUnregistered, channelWritabilityChanged, exceptionCaught, userEventTriggered

Methods inherited from class io.netty.channel.ChannelHandlerAdapter
ensureNotSharable, isSharable

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - logger
```
private static final InternalLogger logger
```
  - releaseMessages
```
private final boolean releaseMessages
```
  - queue
```
private FlowControlHandler.RecyclableArrayDeque queue
```
  - config
```
private ChannelConfig config
```
  - unsatisfiedReads
```
private int unsatisfiedReads
```
    Number of unsatisfied downstream read() calls. A downstream read() is considered unsatisfied if auto-read is off and if it has not yet been paired with a fireChannelRead or a cumulative fireChannelReadComplete.
    A read() can be satisfied in three ways, whichever comes first:
    
    inside the read() call itself, by dequeue()ing a message
    
    in a channelRead()
    
    in a channelReadComplete()
    
    A read() can be satisfied with auto-read on.
    When one or more read() calls are unsatisfied, a downstream channelReadComplete is fired only when either of the following happens:
    
    auto-read is off and unsatisfiedReads returns to zero after dequeue()ing, or
    
    an upstream channelReadComplete arrives
  - dequeuing
```
private boolean dequeuing
```
    true while a dequeue(ChannelHandlerContext) loop is on the stack.
- Constructor Detail
  - FlowControlHandler
```
public FlowControlHandler()
```
  - FlowControlHandler
```
public FlowControlHandler(boolean releaseMessages)
```
- Method Detail
  - isQueueEmpty
```
boolean isQueueEmpty()
```
    Determine if the underlying Queue is empty. This method exists for testing, debugging and inspection purposes and it is not Thread safe!
  - destroy
```
private void destroy()
```
    Releases all messages and destroys the Queue.
  - handlerAdded
```
public void handlerAdded(ChannelHandlerContext ctx)
                  throws java.lang.Exception
```
    Description copied from class: ChannelHandlerAdapter
    
    Do nothing by default, sub-classes may override this method.
    
    Specified by:
    
    handlerAdded in interface ChannelHandler
    
    Overrides:
    
    handlerAdded in class ChannelHandlerAdapter
    
    Throws:
    
    java.lang.Exception
  - handlerRemoved
```
public void handlerRemoved(ChannelHandlerContext ctx)
                    throws java.lang.Exception
```
    Description copied from class: ChannelHandlerAdapter
    
    Do nothing by default, sub-classes may override this method.
    
    Specified by:
    
    handlerRemoved in interface ChannelHandler
    
    Overrides:
    
    handlerRemoved in class ChannelHandlerAdapter
    
    Throws:
    
    java.lang.Exception
  - channelInactive
```
public void channelInactive(ChannelHandlerContext ctx)
                     throws java.lang.Exception
```
    Description copied from class: ChannelInboundHandlerAdapter
    
    Calls ChannelHandlerContext.fireChannelInactive() to forward to the next ChannelInboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.
    
    Specified by:
    
    channelInactive in interface ChannelInboundHandler
    
    Overrides:
    
    channelInactive in class ChannelInboundHandlerAdapter
    
    Throws:
    
    java.lang.Exception
  - read
```
public void read(ChannelHandlerContext ctx)
          throws java.lang.Exception
```
    Description copied from class: ChannelDuplexHandler
    
    Calls ChannelHandlerContext.read() to forward to the next ChannelOutboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.
    
    Specified by:
    
    read in interface ChannelOutboundHandler
    
    Overrides:
    
    read in class ChannelDuplexHandler
    
    Throws:
    
    java.lang.Exception
  - channelRead
```
public void channelRead(ChannelHandlerContext ctx,
                        java.lang.Object msg)
                 throws java.lang.Exception
```
    Description copied from class: ChannelInboundHandlerAdapter
    
    Calls ChannelHandlerContext.fireChannelRead(Object) to forward to the next ChannelInboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.
    
    Specified by:
    
    channelRead in interface ChannelInboundHandler
    
    Overrides:
    
    channelRead in class ChannelInboundHandlerAdapter
    
    Throws:
    
    java.lang.Exception
  - channelReadComplete
```
public void channelReadComplete(ChannelHandlerContext ctx)
                         throws java.lang.Exception
```
    Description copied from class: ChannelInboundHandlerAdapter
    
    Calls ChannelHandlerContext.fireChannelReadComplete() to forward to the next ChannelInboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.
    
    Specified by:
    
    channelReadComplete in interface ChannelInboundHandler
    
    Overrides:
    
    channelReadComplete in class ChannelInboundHandlerAdapter
    
    Throws:
    
    java.lang.Exception
  - dequeue
```
private boolean dequeue(ChannelHandlerContext ctx)
```
    Dequeues messages while auto-read is enabled or downstream reads are unsatisfied, and updates unsatisfiedReads accordingly.
    
    See Also:
    
    read(ChannelHandlerContext), channelRead(ChannelHandlerContext, Object)

Constructor	Description
`FlowControlHandler()`
`FlowControlHandler(boolean releaseMessages)`

Class FlowControlHandler

Nested Class Summary

Nested classes/interfaces inherited from interface io.netty.channel.ChannelHandler

Field Summary

Constructor Summary

Method Summary

Methods inherited from class io.netty.channel.ChannelDuplexHandler

Methods inherited from class io.netty.channel.ChannelInboundHandlerAdapter

Methods inherited from class io.netty.channel.ChannelHandlerAdapter

Methods inherited from class java.lang.Object

Field Detail

logger

releaseMessages

queue

config

unsatisfiedReads

dequeuing

Constructor Detail

FlowControlHandler

FlowControlHandler

Method Detail

isQueueEmpty

destroy

handlerAdded

handlerRemoved

channelInactive

read

channelRead

channelReadComplete

dequeue